Photovoltaic device

ABSTRACT

On a substrate  1  is formed a first transparent electrode layer  3,  on which a p-type semiconductor film  5,  an i-type semiconductor film  6  and an n-type semiconductor film  7  are successively formed to constitute an electric power generating layer. On the n-type semiconductor film  7  is formed a second transparent electrode layer  8,  on which a back electrode layer  9  is formed. Moreover, an intermediate layer  4  made of a given material is formed between the first transparent electrode layer  3  and the p-type semiconductor film  5  to complete a photovoltaic element  40  with high electric power generating efficiency (conversion efficiency).

TECHNICAL FIELD

This invention relates to a photovoltaic element which is preferablyusable as a semiconductor element composing a solar battery and thelike.

BACKGROUND ART

A photovoltaic element which is fabricated by means of vapor phasemethod is promised as a low cost thin film solar battery, and vastresearches and developments are carried out for the photovoltaicelement. As of now, such a photovoltaic element as described hereinafterhas been researched and developed.

FIG. 1 is a structural view illustrating a conventional photovoltaicelement. The photovoltaic element 1 illustrated in FIG. 1 includes asubstrate 1 made of transparent material such as glass, polyethylenenaphtalate (PEN), polyethersulfone (PES), polyethylene terephtalate(PET), a first transparent electrode layer 3 formed on the substrate 1,a p-type semiconductor film 5, an i-type semiconductor film 6 and ann-type semiconductor film 7 which are formed successively on thetransparent electrode layer 3. The p-type semiconductor film 5, thei-type semiconductor film 6 and the n-type semiconductor film 7constitute an electric power generating layer. On the n-typesemiconductor film 7 is formed a second transparent electrode layer 8,on which a back electrode layer 9 is formed of aluminum, silver,titanium or the like.

In the photovoltaic element 10 illustrated in FIG. 1, as designated bythe arrow A, a light is introduced into the photovoltaic element 10 viathe substrate 1, and reflected multiply between the substrate 1 and theback electrode layer 9 to generate an electric power effectively andefficiently at the electric power generating layer constituted by thep-type semiconductor film 5, the i-type semiconductor film 6 and then-type semiconductor film 7.

FIG. 2 is a structural view illustrating another conventionalphotovoltaic element. In FIGS. 1 and 2, same reference numerals aregiven to like or corresponding components. In the photovoltaic element20 illustrated in FIG. 2, on a substrate 11 made of metallic materialsuch as aluminum, silver or titanium are successively formed a firsttransparent electrode 3, an n-type semiconductor film 7, an i-typesemiconductor film 6, an p-type semiconductor film 5 and a secondtransparent electrode layer 8. In this case, as designated by the arrowB, a light is introduced into the photovoltaic element 20 via the secondtransparent electrode layer 8, and reflected multiply between the secondtransparent electrode layer 8 and the substrate 11 to generate anelectric power effectively and efficiently at the electric powergenerating layer constituted by the n-type semi-conductor film 7, thei-type semiconductor film 6 and the p-type semiconductor film 5.

FIG. 3 is a structural view illustrating still another conventionalphotovoltaic element. In FIGS. 1-3, same reference numerals are given tolike or corresponding components. In the photovoltaic element 30illustrated in FIG. 3, a second substrate 2 made of metallic material isformed on a first substrate 1 made of transparent material. On thesecond substrate 2 are successively formed a first transparent electrodelayer 3, an n-type semiconductor film 7, an i-type semiconductor film 6,a p-type semiconductor film 5 and a second transparent electrode film 8.In this case, too, as designated by the arrow C, a light is introducedinto the photovoltaic element 30 via the second transparent electrodelayer 8, and reflected multiply between the transparent electrode layer8 and the first substrate 1; the second substrate 2 to generate anelectric power effective and efficiently at the electric powergenerating layer constituted by the n-type semiconductor film 7, thei-type semiconductor film 6 and the p-type semiconductor film 5.

Herein, in the photovoltaic elements 10, 20 and 30, the p-typesemi-conductor film 5, the i-type semiconductor film 6 and the n-typesemiconductor film 7, which constitute the electric power generatinglayer, are made of amorphous silicon. Into the p-type semiconductor film5 is doped boron, and into the n-type semiconductor film 7 is dopedphosphor.

In the photovoltaic elements 10, 20 and 30 illustrated in FIGS. 1-3,however, the electric power generating efficiencies are not sufficient,so that the photovoltaic elements can not be employed as practical thinfilm solar batteries.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to develop the electric powergenerating efficiency (conversion efficiency) of a photovoltaic elementwhich comprises a substrate, a first transparent electrode layer formedon the substrate, an electric power generating layer formed on the firsttransparent electrode layer, and a second transparent electrode layerformed on the electric power generating layer so that the photovoltaicelement can be employed as a practical thin film solar battery. Herein,the electric power generating layer is constituted by a first conductiontype semiconductor film, an intrinsic semiconductor film, and a secondconduction type semiconductor film different in conduction type from thefirst conduction type semiconductor film which are successively formed.

For achieving the above object, this invention relates to a photovoltaicelement comprising:

-   -   a substrate,    -   a first transparent electrode layer formed on the substrate,    -   an electric power generating layer formed on the first        transparent electrode layer, the electric power generating layer        being constituted by a first conduction type semiconductor film,        an intrinsic semiconductor film and a second conduction type        semiconductor film different in conduction type from the first        conduction type semiconductor film,    -   an second transparent electrode layer formed on the electric        power generating layer, and    -   an intermediate layer made of a given material except oxide        between the first transparent electrode layer and the electric        power generating layer.

The inventors have intensely studied to develop the electric powergenerating efficiencies (conversion efficiencies) of the photovoltaicelements 10, 20 and 30 illustrated in FIGS. 1-3 so that the photovoltaicelements can be employed as a practical thin film solar battery. Then,the inventors have found out that when in the photovoltaic elements 10,20 and 30, instead of the first transparent electrode layer, a metallicelectrode layer is employed, the electric power generating efficienciesof the photovoltaic elements 10, 20 and 30 can be enhanced sufficientlyso that the low electric power generating efficiencies of thephotovoltaic elements 10, 20 and 30 result from the transparentelectrode layer.

As mentioned above, the semiconductor films constituting the electricpower generating layer are made of amorphous silicon by means of plasmaCVD using silane gas and hydrogen gas. In this case, in order to improvethe qualities of the semiconductor films, a larger amount of hydrogengas are employed than the silane gas. Therefore, much hydrogen gas areconverted to reactive hydrogen ions and hydrogen radicals in the plasmaatmosphere.

On the other hand, since the semiconductor films are formed on thetransparent electrode layer, the transparent electrode layer is exposedto the plasma atmosphere containing the hydrogen ions and the hydrogenradicals. As a result, the surface region of the transparent electrodelayer are dissociated into the components thereof. The dissociatedcomponents are partially incorporated in the plasma atmosphere, so thatthe semiconductor films contain the components as impurities in additionto the silane gas elements and the hydrogen gas elements.

Then, particularly, since the transparent electrode layer containsoxygen elements as components, the oxygen elements are partiallycontained in the plasma atmosphere, so that the qualities of thesemiconductor films are deteriorated and thus, the electric powergenerating efficiency of the intended photovoltaic element is alsodeteriorated.

As a result, according to the present invention, the inventors havefound out that by forming an intermediate layer between the transparentelectrode layer as an underlayer and a plurality of semiconductor filmsconstituting the electric power generating layer, the dissociation ofthe transparent electrode layer by the plasma can be prevented. In thiscase, it is considered that the intermediate layer functions as apassivating layer against the plasma.

It is disclosed in Japanese patent application Laid-open No. 2-109375that a tantalum oxide thin film is formed between the transparentelectrode layer and the p-type semiconductor film to function as apassivating film for the transparent electrode layer. It is alsodisclosed in Japanese patent application Laid-open No. 2001-60703 that athin film made of an oxide composed of at least one selected from thegroup consisting of zinc, titanium, antimony, zirconium, silicon,niobium, aluminum, iron or chromium and tin, and having a thickness of1-10% of the thickness of the transparent electrode layer is employed asa protection film for the transparent electrode layer.

Although the thin films disclosed in the conventional techniquescorrespond to the intermediate layer of the photovoltaic element of thepresent invention, if the thin films are employed as the intermediatelayer and the thickness of the intermediate layer is increased in orderto enhance the protecting functions thereof, the resistance of thephotovoltaic element may be increased remarkably, and the variousperformances such as conversion efficiency may be deteriorated. As aresult, even though the conventional thin film is formed as theintermediate layer in order to impart the passivating function to thetransparent electrode layer, the performances of the photovoltaicelement can not be enhanced as designed initially.

Moreover, in order to prevent the dissociation of the transparentelectrode layer by the plasma, various materials are researched anddeveloped for the transparent electrode layer, but not sufficient.

As illustrated in FIG. 1, when the substrate is made of a giventransparent material, and the back electrode layer is formed of ametallic material on the second transparent electrode layer, it isdesired that the intermediate layer is made of a metal composed of atleast one selected from the group consisting of Fe, Ni, Cr, W, Ti, Ag,Ta and Mo or a silicide composed of at least one selected from the groupconsisting of Fe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo (firstphotovoltaic element). In this case, the light is introduced into thephotovoltaic element, and reflected multiply and more effectively, sothat the electric power generating efficiency of the photovoltaicelement can be enhanced, and the performances such as fill factor (FF)of the photovoltaic element can be improved.

Moreover, as illustrated in FIG. 2, when the substrate is made of agiven metallic material, it is desired that the intermediate layer ismade of a metal composed of at least one selected from the groupconsisting of Fe, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo or asilicide composed of at least one selected from the group consisting ofFe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo (second photovoltaicelement). In this case, too, the light is introduced into thephotovoltaic element, and reflected multiply and more effectively, sothat the electric power generating efficiency of the photovoltaicelement can be enhanced, and the performances such as fill factor (FF)of the photovoltaic element can be improved.

In addition, as illustrated in FIG. 3, when the substrate is made of thefirst substrate of a given transparent and the second substrate of agiven metallic material, it is desired that the intermediate layer ismade of a metal composed of at least one selected from the groupconsisting of Fe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo or asilicide composed of at least one selected from the group consisting ofFe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo (third photovoltaicelement). In this case, too, the light is introduced into thephotovoltaic element, and reflected multiply and more effectively, sothat the electric power generating efficiency of the photovoltaicelement can be enhanced, and the performances such as fill factor (FF)of the photovoltaic element can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural view illustrating a conventional photovoltaicelement.

FIG. 2 is a structural view illustrating another conventionalphotovoltaic element.

FIG. 3 is a structural view illustrating still another conventionalphotovoltaic element.

FIG. 4 is a structural view illustrating a photovoltaic elementaccording to the present invention.

FIG. 5 is a structural view illustrating another photovoltaic elementaccording to the present invention.

FIG. 6 is a structural view illustrating still another photovoltaicelement according to the present invention.

FIG. 7 is a graph illustrating high temperature-resistance experimentalresults of the photovoltaic element.

FIG. 8 is a graph illustrating the conversion efficiency (Eff) of thephotovoltaic element and the thickness of the intermediate layer.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail, hereinafter, with referenceto the above drawings.

FIG. 4 is a structural view illustrating a photovoltaic elementaccording to the present invention. Through FIGS. 1-4, same referencenumerals are given to like or corresponding components. The photovoltaicelement 40 illustrated in FIG. 4 includes a substrate 1, a firsttransparent electrode layer 3 formed on the substrate 1, a p-typesemiconductor film 5, an i-type semiconductor film 6 and an n-typesemiconductor film 7 which are formed successively on the transparentelectrode layer 3. The p-type semiconductor film 5, the i-typesemiconductor film 6 and the n-type semiconductor film 7 constitute anelectric power generating layer. On the n-type semiconductor film 7 isformed a second transparent electrode layer 8, on which a back electrodelayer 9 is formed of aluminum, silver, titanium or the like. Moreover,an intermediate layer 4 is formed of a given material except oxidebetween the first transparent electrode layer 3 and the p-typesemiconductor film 5 composing the electric power generating layer.

As mentioned previously, the substrate 1 is made of a transparentmaterial such as polyethylene naphtalate (PEN), polyethersulfone (PES),polyethylene terephtalate (PET). In view of productivity, a film made oforganic resin such as PEN, PES or PET may be preferably employed. Theback electrode layer 8 is made of metallic material such as aluminum,silver or titanium. In this case, the intermediate layer 4 is made of ametal composed of at least one selected from the group consisting of Fe,Ni, Cr, W, Ti, Ag, Ta and Mo or a silicide composed of at least oneselected from the group consisting of Fe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr,W, Ti, Ta and Mo (first photovoltaic element). In this case, the lightis introduced into the photovoltaic element as designated by the arrowA, and reflected multiply and more effectively, so that the electricpower generating efficiency of the photovoltaic element can be enhanced,and the performances such as fill factor (FF) of the photovoltaicelement can be improved.

The p-type semiconductor film 5, the i-type semiconductor film 6 and then-type semiconductor film 7, which constitute the electric powergenerating layer, may be made of amorphous silicon. First of all,therefore, if the intermediate is made of the metallic material asmentioned above and thermally treated, the intermediate layer cancontain silicide through the diffusion of silicon particles from theadjacent electric power generating layer.

The thickness of the intermediate layer 4 is not restricted only if inthe formation of each semiconductor layer of the electric powergenerating layer using plasma CVD, the intermediate layer 4 can functionas a passivating film against the plasma. The upper limit of thethickness of the intermediate layer 4, however, is preferably set to 10nm, and the lower limit of the thickness of the intermediate layer 4 ispreferably set to 0.5 nm, more preferably 2 nm.

In this case, the intermediate layer 4 can function as passivating filmstably, irrespective of the forming method and the forming condition. Ifthe thickness of the intermediate layer 4 is smaller than 0.5 nm, theintermediate layer 4 can not function as a barrier layer againstimpurities such as oxygen elements. If the thickness of the intermediatelayer 4 is larger than 20 nm, the transmissivity of the photovoltaicelement may be deteriorated entirely.

The intermediate layer 4 can be made by means of well known film formingmethod such as sputtering, vacuum deposition or CVD.

As mentioned previously, the p-type semiconductor film 5, the i-typesemiconductor film 6 and the n-type semiconductor film 7, whichconstitute the electric power generating layer, may be made of amorphoussilicon by means of plasma CVD. The semiconductor films 5, 6, and 7 maybe also made of amorphous silicon by means of catalytic CVD usinghot-filament.

With the catalytic CVD method, a raw material gas is contacted with thehot-filament to generate reactive radicals. Therefore, if the reactiveradicals are contacted with the transparent electrode layer 3, thesurface region of the transparent electrode layer 3 is dissociated intocomponents, and thus, the electric power generating efficiency of thephotovoltaic element 40 may be deteriorated due to the dissociatedoxygen elements. As a result, it is turned out that in the formation ofthe electric power generating layer using the catalytic CVD method inaddition to the plasma CVD method, the intermediate layer 4 can functionas a passivating film.

Herein, the thickness of the p-type semiconductor film 5 is set within10-20 nm, and the thickness of the i-type semiconductor film 6 is setwithin 350-450 nm, and the thickness of the n-type semiconductor film 7is set within 20-40 nm.

In the first photovoltaic element, the first transparent electrode layer3 may be made of, e.g., SnO, ITO or ZnO, and the thickness of the firsttransparent electrode layer 3 is set within 60-80 nm. The secondtransparent electrode layer 8 may be also made of, e.g., SnO, ITO orZnO, and the thickness of the second transparent electrode layer 8 isset within 60-80 nm. The thickness of the back electrode layer 9 is setwithin 200-400 nm.

The first transparent electrode layer 3, the second transparentelectrode layer 8 and the back electrode layer 9 may be made by means ofwell known film forming method such as sputtering, vacuum deposition orCVD.

In view of electric power generating efficiency using multiplereflection, particularly, the first transparent electrode 3 ispreferably made of ZnO, and the second transparent electrode 8 ispreferably made of ITO.

FIG. 5 is a structural view illustrating another photovoltaic elementaccording to the present invention. Through FIGS. 1-5, same referencenumerals are given to like or corresponding components. The photovoltaicelement 50 illustrated in FIG. 5 includes a substrate 11, a firsttransparent electrode layer 3 formed on the substrate 11, an n-typesemiconductor film 7, an i-type semi-conductor film 6, a p-typesemiconductor film 5 and a second transparent electrode layer 8 whichare formed successively on the transparent electrode layer 3. Then, anintermediate layer 4 is formed of a given material between the firsttransparent electrode layer 3 and the n-type semiconductor film 7.

As mentioned previously, the substrate 11 is made of a metallic materialsuch as stainless steel, aluminum, silver or titanium. In view ofproductivity, particularly, the substrate 11 is preferably made of astainless foil. In this case, the intermediate layer 4 is made of ametal composed of at least one selected from the group consisting of Fe,Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo or a silicide composed ofat least one selected from the group consisting of Fe, V, Mn, Co, Zr,Nb, Pt, Ni, Cr, W, Ti, Ta and Mo (second photovoltaic element). In thiscase, too, the light is introduced into the photovoltaic element asdesignated by the arrow B, and reflected multiply and more effectively,so that the electric power generating efficiency of the photovoltaicelement can be enhanced, and the performances such as fill factor (FF)of the photovoltaic element can be improved.

The thickness of the intermediate layer 4 is set equal to the one of thefirst photovoltaic element on the same reason and the intermediate layer4 can be made in the same manner as the first photovoltaic element.

The n-type semiconductor film 7, the i-type semiconductor film 6 and thep-type semiconductor film 5, which constitute the electric powergenerating layer, may be made of amorphous silicon by means of plasmaCVD or catalytic CVD. The thickness of the n-type semiconductor film 7is set within 20-40 nm, and the thickness of the p-type semiconductorfilm 5 is set within 350-450 nm, and the thickness of the p-typesemiconductor film 5 is set within 10-20 nm.

The first transparent electrode layer 3 is made of a well knowntransparent material such as SnO, ITO or ZnO, and the thickness of thefirst transparent electrode layer 3 is set within 60-80 nm. The secondtransparent electrode layer 8 is also made of a well known transparentmaterial such as SnO, ITO or ZnO, and the thickness of the firsttransparent electrode layer 3 is also set within 60-80 nm. The firsttransparent electrode layer 3 and the second transparent electrode layer8 may be made by means of well known film forming method such assputtering, vacuum deposition and CVD.

In view of electric power generating efficiency using multiplereflection, the first transparent electrode layer 3 may be preferablymade of ZnO, and the second transparent electrode layer 8 may bepreferably made of ITO.

FIG. 6 is a structural view illustrating still another photovoltaicelement according to the present invention. Through FIGS. 1-6, samereference numerals are given to like or corresponding components. Thephotovoltaic element 60 illustrated in FIG. 6 includes a first substrate1, a second substrate 2 formed on the first substrate 1, and the firsttransparent electrode layer 3 on the second substrate 2. On the firsttransparent electrode layer 3 are successively formed an n-typesemiconductor film 7, an i-type semiconductor film 6, a p-typesemiconductor film 5, and a second transparent electrode layer 8. Aninter-mediate layer 4 is formed of a given material between the firsttransparent electrode layer 3 and the n-type semiconductor film 7.

As mentioned previously, the substrate 1 is made of a transparentmaterial such as polyethylene naphtalate (PEN), polyethersulfone (PES),polyethylene terephtalate (PET). In view of productivity, a film made oforganic resin such as PEN, PES or PET may be preferably employed. Thesecond substrate 2 is made of metallic material such as stainless steel,aluminum, silver or titanium. In view of productivity, the secondsubstrate 2 is preferably made of a stainless foil.

In this case, the intermediate layer 4 is made of a metal composed of atleast one selected from the group consisting of Fe, V, Mn, Co, Zr, Nb,Pt, Ni, Cr, W, Ti, Ta and Mo or a silicide composed of at least oneselected from the group consisting of Fe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr,W, Ti, Ta and Mo (third photovoltaic element). In this case, too, thelight is introduced into the photovoltaic element as designated by thearrow C, and reflected multiply and more effectively, so that theelectric power generating efficiency of the photovoltaic element can beenhanced, and the performances such as fill factor (FF) of thephotovoltaic element can be improved.

The p-type semiconductor film 5, the i-type semiconductor film 6 and then-type semiconductor film 7, which constitute the electric powergenerating layer, may be made of amorphous silicon by means of plasmaCVD or catalytic CVD. The thickness of the n-type semiconductor film 7is set within 20-40 nm, and the thickness of the i-type semiconductorfilm 6 is set within 350-450 nm, and the thickness of the p-typesemiconductor film 5 is set within 10-20 nm.

The first transparent electrode layer 3 is made of a well knowntransparent material such as SnO, ITO or ZnO, and the thickness of thefirst transparent electrode layer 3 is set within 60-80 nm. The secondtransparent electrode layer 8 is also made of a well known transparentmaterial such as SnO, ITO or ZnO, and the thickness of the secondtransparent electrode layer 8 is also set within 60-80 nm. The firsttransparent electrode layer 3 and the second transparent electrode layer8 may be made by means of well known film forming method such assputtering, vacuum deposition and CVD.

In view of electric power generating efficiency using multiplereflection, the first transparent electrode layer 3 may be preferablymade of ZnO, and the second transparent electrode layer 8 may bepreferably made of ITO.

EXAMPLES

This invention will be concretely described on the examples.

Examples 1-3

In these examples, the first photovoltaic element as illustrated in FIG.4 was fabricated. As a substrate was employed a PEN film with athickness of 75 μm, which was set in a DC magnetron sputteringapparatus. Then, a ZnO film was formed as the first transparentelectrode layer in a thickness of 70 nm. The sputtering was performedunder the condition that a ZnO target was employed, and the Ar gaspressured was set to 0.5 Pa, and the input electric power was set to 2.0W/cm².

Then, Ni films were formed as intermediate layers in thicknesses of 2,5, 10 nm by the same DC magnetron sputtering apparatus. The sputteringwas performed under the condition that a Ni-target was employed, and theAr gas pressure was set to 0.5 Pa, and the input electric power was setto 0.5 W/cm².

Then, an electric power generating layer is formed by means of plasmaCVD. The PEN film with the ZnO film and the Ni film was set into theplasma CVD apparatus, and heated to 160° C. Then, a B₂H₆ gas, an H₂ gasand a SiH₄ gas were introduced into the apparatus at flow rates of 0.02sccm, 800 sccm and 4 sccm, respectively, under the condition that thegas pressure was 266.6 Pa, and the input electric power was 180 mW/cm²to form, as the p-type semi-conductor film, a p-type boron-dopedmicro-crystalline silicon film in a thickness of 10 nm.

Then, a SiH₄ gas and an H₂ gas were introduced into the apparatus atflow rates of 50 sccm and 500 sccm, respectively under the conditionthat the gas pressure was set to 266.6 Pa, and the input electric powerwas set to 50 mW/cm² to form, as the i-type semiconductor film, anintrinsic amorphous silicon film in a thickness of 400 nm. Then, a PH₃gas, an H₂ gas and a SiH₄ gas were introduced into the apparatus at flowrates of 0.06 sccm, 500 sccm and 5 sccm, respectively under thecondition that the gas pressure was 133.3 Pa and the input electricpower was 60 mW/cm to form, as the n-type phosphor dopedmicro-crystalline silicon film in a thickness of 30 nm.

Then, the PEN film was set in the DC magnetron sputtering apparatus, andan ITO film was formed as a second transparent electrode layer in athickness of 60 nm. The sputtering was performed under the conditionthat an ITO target was employed, and the Ar gas pressure was set to 0.4Pa, and the oxygen gas pressure was set to 0.08 Pa, and the inputelectric power was set to 0.3 W/cm². Then, an Al film was formed as theback electrode layer under the condition that an Al target was employed,and the Ar gas pressure was set to 0.5 Pa, and the input electric powerwas set to 2.2 W/cm². The conversion efficiencies (Eff), the fillfactors (FF), and the resistances (Rse) along stacking direction of thethus obtained photovoltaic elements were listed in Table 1.

Comparative Example 1

Except that the intermediate layer is not formed, a photovoltaic elementwas formed in the same manner as in Examples 1-3. The conversionefficiency (Eff), the fill factor, and the resistance (Rse) along thestacking direction of the thus obtained photovoltaic element were listedin Table 1. TABLE 1 Thickness of intermediate layer Eff Rse (nm) (%) FF(Ω) Example 1 2 6.26 0.655 25.2 Example 2 5 6.48 0.683 23.3 Example 3 106.62 0.696 20.5 Comparative 0 6.15 0.629 32 Example 1

As is apparent from Table 1, the conversion efficiencies and the fillfactors (FF) of the photovoltaic elements with the Ni films as theintermediate layers relating to Examples 1-3 are increased in comparisonwith the ones of the photovoltaic element without the intermediatelayer, so that the photovoltaic elements with the intermediate layerscan be employed as practical thin film solar batteries.

Herein, the resistances in stacking direction of the photovoltaicelements relating to Examples 1-3 are decreased in comparison with theones of the photovoltaic element relating to Comparative Example 1. Itis, therefore, turned out that the intermediate layer prevents thedissociation of the ZnO transparent electrode layer due to the plasma,and each semiconductor layer composing the electric power generatinglayer is not deteriorated.

When the intermediate layer was made of a Co film or a Ni-50 at % Coalloy film, the same results and phenomena as mentioned above wereobtained. Moreover, when the intermediate layer was made of a Nisilicide film by using a target with Ni:Si atomic ratio=1:2, the sameresults and phenomena as mentioned above were obtained.

Examples 4-6

In these examples, the third photovoltaic element as illustrated in FIG.6 was fabricated. As a substrate was employed a PEN film with athickness of 75 μm, which was set in a DC magnetron sputteringapparatus. Then, an Al film was formed as the second substrate in athickness of 300 nm. The sputtering was performed under the conditionthat an Al target was employed, and the Ar gas pressure was set to 0.5Pa, and the input electric power was 2.2 W/cm². Then, an ZnO film wasformed as the first transparent electrode layer in a thickness of 90 nm.The sputtering was performed under the condition that a ZnO target wasemployed, and the Ar gas pressured was set to 0.5 Pa, and the inputelectric power was set to 2.0 W/cm².

Then, Ni films were formed as intermediate layers in thicknesses of 2,5, 10 nm by the same DC magnetron sputtering apparatus. The sputteringwas performed under the condition that a Ni-target was employed, and theAr gas pressure was set to 0.5 Pa, and the input electric power was setto 0.5 W/cm².

Then, an electric power generating layer is formed by means of plasmaCVD. The PEN film with the ZnO film and the Ni film was set into theplasma CVD apparatus, and heated to 160° C. Then, a. PH₃ gas, an H₂ gasand a SiH₄ gas were introduced into the apparatus at flow rates of 0.06sccm, 500 sccm and 5 sccm, respectively under the condition that the gaspressure was 133.3 Pa and the input electric power was 60 mW/cm² toform, as the n-type semiconductor film, an n-type phosphor dopedmicro-crystalline silicon film in a thickness of 30 nm.

Then, a SiH₄ gas and an H₂ gas were introduced into the apparatus atflow rates of 50 sccm and 500 sccm, respectively under the conditionthat the gas pressure was set to 266.6 Pa, and the input electric powerwas set to 50 mW/cm to form, as the i-type semiconductor film, anintrinsic amorphous silicon film in a thickness of 400 nm.

Then, a B₂H₆ gas, an H₂ gas and a SiH₄ gas were introduced into theapparatus at flow rates of 0.02 sccm, 800 sccm and 4 sccm, respectively,under the condition that the gas pressure was 266.6 Pa, and the inputelectric power was 180 mW/cm² to form, as the p-type semiconductor film,a p-type boron-doped micro-crystalline silicon film in a thickness of 10nm.

Then, the PEN film was set in the DC magnetron sputtering apparatus, andan ITO film was formed as a second transparent electrode layer in athickness of 60 nm. The sputtering was performed under the conditionthat an ITO target was employed, and the Ar gas pressure was set to 0.4Pa, and the oxygen gas pressure was set to 0.08 Pa, and the inputelectric power was set to 0.3 W/cm². The conversion efficiencies (Eff),the fill factors (FF), and the resistances (Rse) along stackingdirection of the thus obtained photovoltaic elements were listed inTable 1.

Comparative Example 2

Except that the intermediate layer is not formed, a photovoltaic elementwas formed in the same manner as in Examples 4-6. The conversionefficiency (Eff), the fill factor (FF), and the resistance (Rse) alongstacking direction of the thus obtained photovoltaic element were listedin Table 2. TABLE 2 Thickness of intermediate layer Eff Rse (nm) (%) FF(Ω) Example 4 2 7.60 1.668 13.3 Example 5 5 7.73 0.683 12 Example 6 106.13 0.72 10.5 Comparative 0 7.44 0.638 23.9 Example 2

As is apparent from Table 2, the conversion efficiencies and the fillfactors of the photovoltaic elements with the Ni films as theintermediate layers relating to Examples 4-6 are increased in comparisonwith the ones of the photovoltaic element without the intermediatelayer, so that the photovoltaic elements with the intermediate layerscan be employed as practical thin film solar batteries.

Herein, the resistances in stacking direction of the photovoltaicelements relating to Examples 4-6 are decreased in comparison with theones of the photovoltaic element relating to Comparative Example 2. Itis, therefore, turned out that the intermediate layer prevents thedissociation of the ZnO transparent electrode layer due to the plasma,and each semiconductor layer composing the electric power generatinglayer is not deteriorated.

When the intermediate layer was made of a Co film or a Ni-50 at % Coalloy film, the same results and phenomena as mentioned above wereobtained. Moreover, when the intermediate layer was made of a Nisilicide film by using a target with Ni:Si atomic ratio=1:2, the sameresults and phenomena as mentioned above were obtained.

Example 7 and Comparative Example 3

Three photovoltaic elements with their respective intermediate layersmade of Ni films were fabricated in the same manner as in Examples 1-3,and three photovoltaic elements with no intermediate layers werefabricated in the same manner as in Comparative Example 1. Then, hightemperature-resistance test at 150° C. was performed for thephotovoltaic elements. The thus obtained results are plotted in FIG. 7.The ordinate axis designates the change ratio of conversion efficiencyas the initial conversion efficiency is set to 1, and the abscissa axisdesignates the testing period (time). As is apparent from FIG. 7, thechange ratio of conversion efficiency of the photovoltaic element withthe intermediate layer is smaller than the one of the photovoltaicelement with no intermediate layer, so that the each semiconductor filmcomposing the electric power generating layer of the photovoltaicelement is not almost deteriorated, and thus, can have long-timereliability.

Comparative Example 4-7

Instead of the Ni intermediate layer, tantalum oxide intermediate layerswith thicknesses of 2 nm and 5 nm were employed, and zirconium oxideintermediate layers with thicknesses of 2 nm and 5 nm were employed, tofabricate photovoltaic elements in the same manner as in Examples 1-3.The conversion efficiencies(Eff), the fill factors (FF), and theresistances (Rse) along stacking direction of the thus obtainedphotovoltaic elements were listed in Table 3, in comparison with theresults relating to Examples 1-3. Then, the dependence of the conversionefficiency on the thickness of the intermediate layer was illustrated inFIG. 8. TABLE 3 Thickness of intermediate layer (nm) Eff FF Rse Niintermediate layer 0 6.15 0.619 32 2 6.26 0.655 25.2 5 6.48 0.683 23.310 6.62 0.696 20.5 Tantalum oxide intermediate layer 0 2 6.32 0.648 28.15 5.64 0.592 43.9 10 Zirconium oxide intermediate layer 0 2 5.87 0.61131.2 5 5.18 0.532 48.7 10

As is apparent from Table 3 and FIG. 8, in the use of the tantalum oxideintermediate layer and the zirconium oxide intermediate layer, as thethickness of the intermediate layer is increased, the intermediate layerfunctions as a passivating film more effectively, but the resistance(Rse) in stacking direction of the photovoltaic element is increased,and thus, the conversion efficiency (Eff) of the photovoltaic element isdeteriorated. Particularly, as the thickness of the intermediate layeris increased to 5 nm, the conversion efficiency of the photovoltaicelement is deteriorated in comparison with the one of the photovoltaicelement with no intermediate layer. Moreover, in the use of thezirconium oxide intermediate layer, as the thickness of the intermediatelayer is increased only to 2 nm, the conversion efficiency (Eff) of thephotovoltaic element is deteriorated, and thus, the performances of thephotovoltaic element is not enhanced.

Although the present invention was described in detail with reference tothe above examples, this invention is not limited to the abovedisclosure and every kind of variation and modification may be madewithout departing from the scope of the present invention. For example,in the photovoltaic element illustrated in FIG 1, the first conductiontype semiconductor layer is made of the p-type semiconductor film, andthe second conduction type semiconductor layer is made of the n-typesemiconductor film, but the other way round will do.

Industrial Applicability

According to the present invention, in the photovoltaic elementcomprising the substrate, the first transparent electrode layer formedon the substrate, the electric power generating layer formed on thefirst transparent electrode layer, and the second transparent electrodelayer formed on the electric power generating layer, the electric powergenerating layer being constituted by the first conduction typesemiconductor film, the intrinsic semiconductor film and the secondconduction type semiconductor film different in conduction type from thefirst conduction type semiconductor film which are successively formed,since the intermediate layer is formed between the first transparentelectrode layer and the electric power generating layer, the qualitiesof the first conduction type semiconductor film, the intrinsicsemiconductor film and the second conduction type semiconductor filmconstituting the electric power generating layer are not deteriorated,and thus, the electric power generating efficiency (conversionefficiency) of the photovoltaic element can be enhanced. Therefore, thephotovoltaic element can be preferably usable as a practical solarbattery.

1. A photovoltaic element comprising: a substrate, a first transparentelectrode layer formed on said substrate, an electric power generatinglayer formed on said first transparent electrode layer, said electricpower generating layer being constituted by a first conduction typesemiconductor film, an intrinsic semiconductor film and a secondconduction type semiconductor film different in conduction type fromsaid first conduction type semiconductor film, an second transparentelectrode layer formed on said electric power generating layer, and anintermediate layer made of a given material except oxide between saidfirst transparent electrode layer and said electric power generatinglayer.
 2. The photovoltaic element as defined in claim 1, wherein athickness of said intermediate layer is set within 0.5-20 nm.
 3. Thephotovoltaic element as defined in claim 1, further comprising a backelectrode layer on said second transparent electrode layer, wherein saidsubstrate is made of a given transparent material and said intermediatelayer is made of a metal composed of at least one selected from thegroup consisting of Fe, Ni, Cr, W, Ti, Ag, Ta and Mo or a silicidecomposed of at least one selected from the group consisting of Fe, V,Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo.
 4. The photovoltaicelement as defined in claim 3, wherein said substrate is made of anorganic film.
 5. The photovoltaic element as defined in claim 1, whereinsaid substrate is made of a given metallic material and saidintermediate layer is made of a metal composed of at least one selectedfrom the group consisting of Fe, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Taand Mo or a silicide composed of at least one selected from the groupconsisting of Fe, V, Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo. 6.The photovoltaic element as defined in claim 5, wherein said substrateis made of a stainless foil.
 7. The photovoltaic element as defined inclaim 1, wherein said substrate is composed of a first substrate made ofa given transparent material and a second substrate made of a givenmetallic material, and said intermediate layer is made of a metalcomposed of at least one selected from the group consisting of Fe, V,Mn, Co, Zr, Nb, Pt, Ni, Cr, W, Ti, Ta and Mo or a silicide composed ofat least one selected from the group consisting of Fe, V, Mn, Co, Zr,Nb, Pt, Ni, Cr, W, Ti, Ta and Mo.
 8. The photovoltaic element as definedin claim 7, wherein said first substrate is made of an organic film. 9.The photovoltaic element as defined in claim 7, wherein said secondsubstrate is made of a stainless foil.
 10. The photovoltaic element asclaim 1, wherein said first transparent electrode film is made of a ZnOfilm.
 11. The photovoltaic element as claim 1, wherein said secondtransparent electrode film is made of an ITO film.
 12. The photovoltaicelement as claim 1, wherein said electric power generating layer isformed by means of plasma CVD.
 13. The photovoltaic element as claim 1,wherein said electric power generating layer is made of amorphoussilicon.